(a) Field of the Invention
The present invention relates to a process for preparing a block copolymer of a monoolefin and a vinyl compound, a vinylidene compound or a lactone. More specifically, it relates to a process for preparing the above-mentioned block copolymer in accordance with a living polymerization method by the use of a specific catalyst.
(b) Description of the Prior Art
In general, a polyolefin is poor in chemical reactivity and adhesive properties to another resin, is hardly dyed with a dye or a pigment, and has a large gas permeability.
In order to solve these problems, it has been carried out to graft-polymerize a monomer having a polar group to a polyolefin.
Alternatively, as another method, it has already been reported by the same inventors as in this application that by the use of a lanthanoide catalyst, methyl methacrylate or a lactone can be further block-copolymerized to a polymerization-active terminal at which ethylene is polymerized (Japanese Patent Application Laid-open No. 255116/1991 & which corresponds to U.S. Pat. Nos. 5,132,369 and 5,218,064). This publication discloses that according to the above method, the block copolymer of ethylene and the vinyl compound or the lactone can be prepared, but a block copolymer of an .alpha.-olefin having 3 or more carbon atoms and a vinyl compound or a lactone is not disclosed anywhere. The polymerization of ethylene is relatively simple, and a copolymer with ethylene can also easily be prepared. For example, the ethylene copolymer can easily be prepared even in accordance with a radical polymerization method. As random copolymers, copolymers of ethylene-acrylate, ethylene-vinyl acetate and the like have been industrially produced in large quantities. However, if the preparation of a copolymer by the use of an .alpha.-olefin of 3 or more carbon atoms such as propylene is intended in accordance with a similar procedure, the molecular weight of the obtained copolymer is low, and for this reason, it is very difficult to obtain the useful copolymer. Thus, any effective method has not been known. In the above-mentioned patent, the block copolymer of ethylene has been disclosed, but copolymer of an .alpha.-olefin having 3 or more carbon atoms is neither disclosed nor suggested anywhere.
The method disclosed in the above-identified Patent cannot polymerize an .alpha.-olefin having 3 or more carbon atoms, such as propylene, and therefore the method is not capable of obtaining a block copolymer of an .alpha.-olefin having 3 or more carbon atoms and a vinyl compound or a lactone.